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The stuff they use to insulate houses is definitely stronger than the spray foam like great stuff they sell at the hardware store. I used some to fill in a missing piece of foam on a bic board that I picked up to use as a summer beater board. It has held up for several years now and I have let it get smashed on shore break a lot. It is a little more protected being on a bic board then on a more traditional style glassed board. I still think you should give it a shot. Worst case scenario you only get one session out of the thing.

Koki, you may be thinking of Great Stuff spray foam. You're right, that's not as dense. The stuff they use in house wall cavities is much more dense and ends up being more the density of those solid foam insulation panels when it's cured.

Yes, Zippy--it is poly based but there are also some products that use more natural ingredients.

Cool stuff, expensive as all get out and I would never use it in a surfboard. Plus, my favorite insulation is the blown-in recycled newspaper and denim. It's more fire retardant than the foam stuff.

This stuff would not work. There is a reason why Clark Foam, US Blanks, Walker, etc. try to keep their formulas a secret. This stuff is just a basic polyester foam, which you can buy in a 2 part mixture from most fiberglass suppliers. With making blanks its all about controlling certain factors to yield a blank suitable enough for a surfboard.

First off building a mold without anything other than rebar reinforced concrete is asking for trouble. There was a huge argument last month on Swaylocks with a guy trying to do this same exact thing. He built his with fiberglass and made a metal skeleton around it. A lot of guys, even the gurus of the industry said he was nuts. WHen you see the molds that the blank companies use you will understand why it has to be concrete. Blowing foam in wall sections is one thing, but placing it in an air tight mold the amount of pressure created will explode the mold. This is something you don't want to be around when it does, the early blank makers found that out the hard way with clamps exploding & flying all over the room.

Second this foam will most likely have a lot of voids & air pockets in it which is unacceptable for shaping. This was a problem in early foam blanks & they now use a special paper that they line the molds with to prevent such air bubbles from occurring.

It is always going to be cheaper, easier, & cleaner to just buy a blank from the guys that already have it figured out. Its definitely a cool idea but one that just would be too dangerous & expensive in the end to do.

if you do it make sure it is a closed cell foam. open cell absorbs water worse than a surfboard blank. With closed cell foam water absorbtion is non existant. You should see what it looks like when you have to remove open cell foam from a wall cavity or basement after a flood. you can wring it out like a dish sponge.
Density of closed cell foam is about 2 to 3 pounds per cubic ft dependent on the mix which you have to do your self, it degrades very fast when exposed to UV light and you need a face shield and a respirator when you spray it. it is not something you want in your eyes on your skin or in your lungs. the smallest kit you can buy is 20 board feet which is 20 sq ft at 1 inch thick. it is not made to be injected into an enclosed cavity because of the expansion. but that pertains to blowing out drywall.

what you could do if you decide to insulate with foam( which is a great insulating and airsealing material by the way) is have a mold ready and when they come do the install have the professional inject some into the mold. they probably wouldn't charge you. use something stronger than paper as the mold.

the sample this guy left me does not seem like something that couldnt be used.... its hard, it floats, the cut sample doesnt not show any voids in the body and it doesnt absorb water... so I guess its closed cell. also the video samples are showing them putting it into closed chambers with no ill effects...
I really think Im going to see about trying this when I get the time(which means I might never do it!)... could be a fun project. I'd have to find someone to glass it for me though!!!

The wall section they are putting the foam in is not closed, because there is the hole in the wall in which they place the hose through giving an outlet for foam & gases to escape. Another thing to keep in mind is the density of the foam throughout. In surfboard blanks the farther you go into the core of the foam the softer it gets. Although this foam may be hard on the outside, the more you start to shape the foam it could reveal a soft core. Not trying to be negative just trying to give some information to better help you understand the process.